The present invention relates to an electron emitting device for emitting electrons using an appropriate material (for example, diamond particles) as an electron emitting source (emitter), a method for producing the same, and an image display apparatus including such an electron emitting device, and a method for producing such an image display apparatus. The present invention also relates to a method for driving the electron emitting device.
Recently, microscopic electron emitting devices have actively been developed as electron emitting sources for thin display devices and as emitters of microscopic vacuum devices capable of a high-speed operation. Conventionally used electron emitting devices are of a xe2x80x9cheat releasing typexe2x80x9d, which applies a high voltage to a material, such as tungsten, heated to a high temperature. Recently, research and development of xe2x80x9ccold cathode typexe2x80x9d electron emitting devices which do not need to be heated to a high temperature and thus can emit electrons even at a low voltage have actively been performed.
Cold cathode type electron emitting devices (hereinafter, also referred to as xe2x80x9ccold cathode devicesxe2x80x9d) are required to be driven at a low voltage and a low power consumption and to stably obtain a large amount of current. As such a cold cathode type electron emitting device, a device using diamond for an electron emitting region (emitter) has recently been proposed. Such a device has been proposed utilizing the facts that diamond is a semiconductor material having a wide forbidden band (5.5 eV); has very suitable characteristics for a material for an electron emitting device such as, for example, a high hardness, a high resistance against wearing, a high heat conductivity, and chemical inactivity; and can obtain a negative electron affinity by controlling a surface state to make the energy level of the end of the conduction band lower than the energy level of the vacuum area. Especially, the characteristic of the negative electron affinity means that electrons can easily be emitted by injecting electrons into the conduction band of diamond.
An electron emitting device using diamond is disclosed in, for example, Japanese Laid-Open Publication No. 7-282715. A structure disclosed in the publication is shown as simplified in FIG. 29.
Specifically in the structure shown in FIG. 29, a conductive layer 1112 acting as an electrode is formed on a substrate 1111, and an electron emitting region 1114 formed of diamond particles 1113 is formed on the conductive layer 1112. Each of the diamond particles 1113 has a negative electron affinity as a result of a prescribed treatment. A counter electrode (not shown) is provided so as to face the electron emitting region 1114 formed of the diamond particles 1113. Electrons are emitted from each diamond particle 1113 by supplying the counter electrode with a potential.
In the conventional structure shown in FIG. 29, the electron affinity of a surface of the diamond particles 1113 is negative. Accordingly, the electrons migrating into the diamond particles 1113 from the conductive layer 1112 should be easily emitted from the diamond particles 1113. Therefore, theoretically, electrons can be emitted from the diamond particles 1113 without application of a high voltage to the counter electrode (not shown).
However, in actuality, a high voltage as in a previous structure needs to be applied to the counter electrode in order to cause electrons to emit with the structure shown in FIG. 29.
The present invention made in light of the above-described problem of the conventional art has objectives of providing (1) an electron emitting device capable of stably providing a large amount of current when driven at a low voltage and a method for producing the same, (2) an image display apparatus including such an electron emitting device and a method for producing the same, and (3) a method for driving such an electron emitting device.
An electron emitting device according to the present invention includes at least comprising an electron transporting member; an electron emitting member; and an electric field concentration region formed between the electron transporting member and the electron emitting member.
The electron transporting member may be a conductive layer.
The electric field concentration region may be formed of an insulating layer.
The electron emitting member may be formed of particles.
In one embodiment, the electron transporting member is a conductive layer, the electric field concentration region is formed of an insulating layer formed on the conductive layer, and the electron emitting member is formed of particles provided on the insulating layer.
In one embodiment, the electron emitting device further includes an extraction electrode provided at a prescribed position with respect to the electron emitting member and supplied with a potential for extracting electrons from the electron emitting member.
In one embodiment, a surface of the electron transporting member is roughened so as to have convex and concave portions, and the electron emitting member is provided on the roughened surface of the electron transporting member, with at least the convex portions of the convex and concave portions interposed therebetween.
In one embodiment, the electron emitting device further includes a circuit for causing an electric current to flow in the electron transporting member.
In one embodiment, the electric field concentration region is formed of an insulating layer formed on a surface of the particles forming the electron emitting member, and the particles are provided on the electron transporting member with the insulating layer interposed therebetween.
In another embodiment, the electron transporting member is a conductive layer, and the electric field concentration region is formed of an insulating layer formed on the conductive layer, and the electron emitting member is formed of particles provided so as to be partially buried in the insulating layer.
Preferably, the electric field concentration region has a thickness of 1000 xc3x85or less.
In one embodiment, the electron emitting member is formed of a plurality of particles provided independently, out of contact with one another.
Preferably, the electron emitting member in formed of particles of a material having a negative electron affinity.
The particles may be diamond particles. For example, the diamond particles are artificial diamond particles. Alternatively, the diamond particles are diamond particles synthesized by a vapor phase technique.
Alternatively, the particles are carbon particles partially having a diamond structure.
An outermost surface layer of the diamond particles may have a termination structure bonded with hydrogen.
For example, the diamond particles are formed by being exposed to a hydrogen atmosphere of 600xc2x0 C. or higher.
The diamond particles may include an impurity.
The impurity may be formed by ion implantation. Preferably, the impurity has a density of 1xc3x971013/cm3 or higher.
The electron transporting member may be a conductive layer formed of a material having a small work function.
An electron emitting device according to another aspect of the invention includes at least comprising an electron injection member; an electron emitting member; and an electron transporting member formed between the electron transporting member and the electron emitting member. The electron transporting member includes an electrically insulating or highly resistive portion when supplied with a prescribed low DC voltage.
Preferably, the electron transporting member includes a portion having an electric resistance of 1 kxcexa9cm or higher when supplied with such a weak electric field as to make a highest electric field strength in the electron transporting member 1 mV/xcexcm or less.
The electron emitting member may include a substance having a negative electron affinity.
The electron emitting member may include a substance containing at least carbon or particles thereof. For example, the electron emitting member may include graphite particles.
In one embodiment, the electron emitting member includes at least wide bandgap semiconductor particles having a bandgap of 3.5 eV or more.
For example, the electron emitting member includes diamond particles.
In one embodiment, the electron emitting member is formed of particles, and the particles are each larger than a cube having a side of 1 nm and can be accommodated in a cube having a side of 1 mm.
In one embodiment, the electron transporting member is formed of particles or a thin film of a wide bandgap semiconductor material having a bandgap of 3.5 eV or more, and the electron emitting member is formed on a surface of the particles or the thin film of the wide bandgap semiconductor material.
In one embodiment, the electron transporting member and the electron emitting member are each formed of particles of a thin film of a diamond material formed by a vapor phase growth technique.
The electron emitting member may be a surface conductive layer of particles or a thin film of a hydrogenized diamond material.
In one embodiment, the electron transporting member and the electron emitting member are each formed of a diamond thin film, and the diamond thin film has a thickness of 10 nm or more and 10 xcexcm or less.
In one embodiment, the electron transporting member is formed of diamond particles, and the electron emitting member is formed of diamond-containing a carbon-based thin film or particles formed on at least a part of a surface of the diamond particles forming the electron transporting member.
In one embodiment, at least one of the electron emitting member and the electron transporting member is formed of a wide bandgap semiconductor material having a bandgap of 3.5 eV or more, and the wide bandgap semiconductor material is a compound of nitrogen and at least one element of Ga, Al, In and B.
Preferably, the electron injection member and the electron transporting member are in ohmic contact with each other.
The electron transporting member includes an insulating layer having a thickness of 500 nm or less.
A method for producing an electron emitting device according to the present invention includes the steps of forming an electron transporting member on a substrate; and providing an electron emitting member in contact with the electron transporting member with an electric field concentration region interposed therebetween.
In one embodiment, the electron transporting member is a conductive layer formed on the substrate, and the electron emitting member is formed of particles provided in contact with the conductive layer with an insulating layer acting as the electric field concentration region interposed therebetween.
In one embodiment, the method further includes the step of providing an extraction electrode to be supplied with a potential for extracting electrons from the electron emitting member, the extraction electrode being provided at a prescribed position with respect to the electron emitting member.
In one embodiment, the method further includes the step of roughening a surface of the electron transporting member.
In one embodiment, the method further includes the step of providing a circuit for causing an electric current to flow in the electron transporting member.
In one embodiment, the step of providing the electron emitting member includes the steps of forming an insulating layer acting as the electric field concentration region on a conductive layer acting as the electron transporting member, and providing particles acting as the electron emitting member on the insulating layer.
In one embodiment, the step of providing the electron emitting member includes the steps of forming an insulating layer acting as the electric field concentration region on a surface of particles acting as the electron emitting member, and providing the particles on a conductive layer acting as the electron transporting member.
In one embodiment, the step of providing the electron emitting member includes the steps of causing a mixture of a liquid curable insulating substance and prescribed particles to adhere to a conductive layer acting as the electron transporting member, curing the liquid curable insulating substance, and selectively removing only a surface portion of the cured insulating substance to expose a portion of the particles included in the mixture, thereby causing the exposed portion of the particles to act as the electron emitting member.
The selective removing step can be performed by chemical etching. For example, the chemical etching is performed by a hydrogen plasma irradiation process.
In one embodiment, the step of providing the electron emitting member includes the steps of forming an insulating layer acting as the electric field concentration region on a conductive layer acting as the electron transporting member, providing the substrate having the insulating layer formed thereon in a solution containing particles dispersed therein, and applying ultrasonic vibration to the solution to cause the particles in the solution to adhere to the insulating layer. The particles adhering to the insulating layer act as the electron emitting member.
In one embodiment, the step of providing the electron emitting member includes the steps of forming an insulating layer acting as the electric field concentration region on a conductive layer acting as the electron transporting member, and applying a solution containing particles dispersed therein to the insulating layer to cause the particles to adhere to the insulating layer. The particles adhering to the insulating layer act as the electron emitting member.
In one embodiment, the step of providing the electron emitting member includes the steps of forming an insulating layer acting as the electric field concentration region on a conductive layer acting as the electron transporting member, and using an electrophoresis process using a solution containing particles dispersed therein to cause the particles to adhere to the insulating layer. The particles adhering to, the insulating layer act as the electron emitting member.
In one embodiment, the step of providing the electron emitting member includes the steps of forming an insulating layer acting as the electric field concentration region on a surface of particles acting as the electron emitting member, providing the substrate having a conductive layer acting as the electron transporting member formed thereon in a solution containing particles dispersed therein, and applying ultrasonic vibration to the solution to cause the particles in the solution to adhere to the conductive layer.
In one embodiment, the step of providing the electron emitting member includes the steps of forming an insulating layer acting as the electric field concentration region on a surface of particles acting as the electron emitting member, and applying a solution containing particles dispersed therein to the conductive layer acting as the electron transporting member to cause the particles to adhere to the insulating layer.
In one embodiment, the stop of providing the electron emitting member includes the steps of forming an insulating layer acting as the electric field concentration region on a surface of particles acting as the electron emitting member, and using an electrophoresis process using a solution containing the particles dispersed therein to cause the particles to adhere to a conductive layer acting as the electron transporting member.
In one embodiment, the step of roughening the surface of the electron transporting member includes the step of forming a conductive layer acting as the electron transporting member by a thermal spraying technique.
In one embodiment, the step of roughening the surface of the electron transporting member includes the steps of forming a flat conductive layer acting as the electron transporting member, and roughening a surface of the flat conductive layer. For example, the step of roughening a surface of the flat conductive layer is performed by blasting. Alternatively, the step of roughening a surface of the flat conductive layer is performed by chemical etching.
In one embodiment, the method further includes the step of roughening a surface of the substrate, wherein the electron transporting member is formed on the roughened surface of the substrate to roughen a surface of the electron transporting member.
In one embodiment, at least one of the electron transporting member and the electron emitting member is a diamond thin film grown by a vapor phase growth technique, the method comprising the step of distributing diamond growth nuclei having a distribution density of 1xc3x971010/cm2 or more as a pre-vapor phase technique.
According to still another aspect of the invention, a method for driving an electron emitting device, the electron emitting device including at least an electron injection member, an electron emitting member, and an electron transporting member between the electron injection member and the electron emitting member. The electron transporting member includes an electrically insulating or highly resistive portion when supplied with a prescribed low DC voltage, the method comprising the step of applying a potential changing time-wise to the electron emitting member.
Preferably, a potential changing time-wise is applied to the electron emitting member in the state where the electron emitting member is insulated from the electron injection member in a DC manner.
In one embodiment, the potential changing time-wise is formed by superimposing a DC voltage for causing the electron emitting member to have a positive potential with respect to the electron injection member, to a prescribed AC voltage.
In one embodiment, an extraction electrode is supplied with a DC voltage, for applying an electric field to the electron emitting member through a vacuum area, the electric field being applied for causing electrons to be emitted from the electron emitting member, so that the electron injection member has a negative potential and the extraction electrode has a positive potential.
An image display apparatus according to the present invention includes at least an electron emitting source; and an image forming section for forming an image by electrons emitted from the electron emitting source. The electron emitting source includes at least a plurality of electron emitting devices. Each of the plurality of electron emitting devices has features as described above.
A method for producing an image display apparatus according to the present invention includes the steps of forming a plurality of electron emitting devices; forming an electron emitting source using the plurality of electron emitting devices and providing the electron emitting source at a prescribed position; and providing an image forming section for forming an image by electrons emitted from the electron emitting source, at a prescribed positional relationship with the electron emitting source. Each of the plurality of electron emitting devices is formed by a method according to the present invention having features as described above.